a) Field of the Invention
The present invention relates to smelting reduction process and, more particularly, to a smelting reduction apparatus which separates exhaust gas, which is exhausted from a melter-gasifier or a fluidized bed reactor, into dusts and reducing gas to supply them to a corresponding fluidized bed reactor respectively.
(b) Description of the Related Art
Generally, a blast furnace has been extensively used to make iron through reducing and melting iron ores. However, the blast furnace involves a drawback that the charging materials should be pre-treated to bear is agglomerated forms such as sintered iron ores and cokes.
In order to solve such a problem, a smelting and reduction process has been developed for the direct use of fine iron ores and coal without pretreatment.
The smelting reduction process is composed of a preliminary reduction process and a final reduction process. In the preliminary reduction process, the charged fine iron ores are pre-heated and then preliminarily reduced. In the final reduction process, a sponge iron which is reduced in the preliminary reduction process is finally reduced and melted in the presence of high pressure oxygen and coal to thereby form a molten iron.
The fluidized bed reduction reactor (hereinafter, referred to xe2x80x9cfluidized bed reactorxe2x80x9d) is used as an equipment for the preliminary reduction process, and a melter-gasifier is used as an equipment for the final reduction process.
The preliminary reduction process is typically divided into a moving bed type and a fluidized bed type according to a contact state between raw iron ores and reducing gas. It is efficient to apply the fluidized bed type preliminary reduction process rather than the moving bed type if the charged iron ore has a small particle size and a wide particle size distribution.
Korean Patent No. 117065 discloses an apparatus for such a fluidized bed type preliminary reduction process. According to this patent, a device for uniformly reducing a fine iron ore having a wide particle size distribution in a fluidized bed reactor is proposed. In order to achieve such a uniform reducing of the fine iron ore, the patent provides a three-stage type fluidized reactor which is designed in a conical shape having a wide upper part and a narrow lower part, wherein the iron ore is reduced through three stages of pre-heating, pre-reducing and final preliminary reducing. This patent also proposes a cyclone for collecting fine iron ore, which is discharged, from an upper part of the respective fluidized bed reactors by scattering to supply to a bottom part of the respective fluidized bed reactors.
According to this patent designed as above, the fine iron ore having the wide particle size distribution may be efficiently reduced while maintaining stable fluidized state.
This patent has, however, a disadvantage that a gas distributor of the fluidized bed reactors may be clogged by dusts dust contained in the reducing gas. That is, a large amount of dusts is included in exhaust gas, which is discharged from the melter-gasifier and supplied to the fluidized bed reactors. If the dusts are supplied to the gas distributor of a final reduction furnace, the dust becomes stuck to nozzles, which are mounted in the gas distributor, and if the sticking phenomenon is accumulated, the gas distributor itself becomes clogged.
If the gas distributor is clogged as above, it becomes impossible to maintain a uniform flow of the reducing gas in the fluidized bed reactors, and more severely, operations should be stopped.
Therefore, the present invention is derived to resolve the above disadvantages and problems of the related art and has an object to provide a smelting and reduction apparatus which can separate exhaust gas, which is exhausted from a melter-gasifier or a fluidized bed reactor, into dusts and reducing gas to supply them to each fluidized bed reactor respectively.
It is another object of the present invention to provide a method for manufacturing molten pig iron by a smelting and reduction process, which can prevent sticking of particles of fine iron ores and clogging of a gas distributor by coating separated dusts on a surface of the particles of the fine iron ores which is flowing in the fluidized bed reactors.
This and other objects may be achieved by the present invention, which is described in detail hereinafter.
According to one aspect of the present invention, a smelting and reduction apparatus includes a three-stage type fluidized reactor, a melter-gasifier for manufacturing molten pig iron by finally reducing fine iron ores of which reaction is finished in a final fluidized reactor, and a dust separating device, which performs separation of exhausted gas from the melter-gasifier into dusts and reducing gas so as to supply the separated reducing gas to a lower part of the final fluidized bed reactor, dusts having a larger particle sizes in the separated dusts to the melter-gasifier again, and fine dusts having a smaller particle sizes in the separated dusts to an upper part of a gas distributor of the final fluidized bed reactor.
The three-stage type fluidized bed reactor of the present invention includes a) an or e charging duct mounted on a side of respective fluidized bed reactors for charging fine iron ores, b) a gas supply duct mounted at a lower part of the respective fluidized bed reactors, c) an ore discharge duct mounted on a side wall of the respective fluidized bed reactors for discharging fine iron ores which are charged into the respective fluidized bed reactors and reactions thereof are finished, d) a gas distributor mounted in the respective fluidized bed reactors for uniformly dispersing reducing gas into the respective fluidized bed reactors, and e) a cyclone for separating fine iron ore particles from the reducing gas, which is discharged from the upper parts of the respective fluidized bed reactors, to supply the reducing gas to next reactor or discharge outside and recycle the fine iron ore particles to the lower parts of the respective fluidized bed reactors.
In the present invention, each fludized bed reactor is manufactured in a dual-stage cylindrical shape of which a diameter of a lower part is small and a diameter of an upper part is large so that lower and the upper parts are to connected to each other slantingly. In the dual-stage cylindrical fluidized bed reactors, the diameter of the upper cylindrical part is larger than that of the lower cylindrical part by 1.5xcx9c2.0 times, and the inclination of the connection between the upper and lower cylindrical parts is 20xcx9c30xc2x0 with relation to a central axis of the fluidized bed reactors. A whole height of the fluidized bed reactors is larger than a diameter of the lower cylindrical part by 10xcx9c20 times.
In the present invention, the dust separation device is formed of at least two or more cyclones and at least one or more dust storage bins. A first cyclone of the cyclones is connected to the upper part and the lower part of the melter-gasifier and an upper part of a second cyclone. The second cyclone is connected to the lower part of the final fluidized bed reactor and an upper part of the dust storage bin and the dust storage bin is connected to an upper part of the gas distributor of the final fluidized bed reactor.
In the dust separation device, the second cyclone and the dust storage bin is connected by a dust supply duct which is mounted with a two-way valve, wherein the dust supply duct branched by the two-way valve is connected to a dust supply duct which connects the first cyclone and the melter-gasifier.
The dust storage bin part is formed of three dust storage bins respectively connected to one another via the dust supply ducts. The dust supply duct which is positioned at a lower part of a first dust storage bin is mounted with a nitrogen gas injection device, so that dusts stored in the first dust storage bin can be pneumatically transported to a second dust storage bin with high pressure nitrogen gas. A dust supply duct which is positioned at a lower part of a third dust storage bin is also mounted with a nitrogen gas injection device, so that the dusts stored in the third dust storage bin can be introduced into the final reactor with high pressure nitrogen gas.
On the other hand, a dust supply duct connecting the lower part of the third dust storage bin to the nitrogen gas injection device is mounted with a dust introducing feeder for controlling the amount of dust supply to the final reactor. Further, each of the dust supply ducts is mounted with a control valve for controlling a supply of the dusts conveyed to the dust supply ducts.
The molten pig iron is manufactured from the fine iron ores by using the smelting reduction apparatus hereinabove.
The process for manufacturing the molten pig iron by using the smelting reduction apparatus of the present invention is characterized in that the exhaust is gas discharged from the melter-gasifier is separated into reducing gas and dusts to be supplied to the final fluidized bed reactor.
Even though the separated reducing gas is directly supplied to the lower part of the final fluidized bed reactor, the dusts are separated again such that the fine dusts having a smaller particle size is blown into the upper part of the gas distributor of the final fluidized bed reactor by high pressure nitrogen.
As the fine dusts are blown into the fluidized bed reactor, the fine dusts are coated on surfaces of the fine iron ores, so that the sticking between the fine iron ores and the gas distributor may be prevented.
The pressure of the nitrogen for the injection of dust particles is controlled higher than an internal pressure of the final fluidizing bed reactor by 2xcx9c3 times.
A velocity of the reducing gas in the respective fluidizing bed reactors is preferably controlled 1.2xcx9c1.5 times of a minimum fluidizing velocity of the fine iron ores residing in the fluidizing bed reactors.
If the molten pig iron is manufactured by the process described hereinabove, the sticking between the fine iron ores and the gas distributor may be prevented, thereby effectively preventing operation obstacles of the smelting reduction process.